Fix gcc uninitialized variable warnings

Gcc -Wall warn: 'uninitialized variable'

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

cmd/zdb/zdb.c

@@ -2888,7 +2888,7 @@ find_zpool(char **target, nvlist_t **configp, int dirc, char **dirv)
 	nvlist_t *match = NULL;
 	char *name = NULL;
 	char *sepp = NULL;
-	char sep;
+	char sep = 0;
 	int count = 0;
 	importargs_t args = { 0 };
 

cmd/zfs/zfs_main.c

@@ -671,7 +671,7 @@ zfs_do_create(int argc, char **argv)
 {
 	zfs_type_t type = ZFS_TYPE_FILESYSTEM;
 	zfs_handle_t *zhp = NULL;
-	uint64_t volsize;
+	uint64_t volsize = 0;
 	int c;
 	boolean_t noreserve = B_FALSE;
 	boolean_t bflag = B_FALSE;
@@ -4060,7 +4060,7 @@ int
 main(int argc, char **argv)
 {
 	int ret;
-	int i;
+	int i = 0;
 	char *progname;
 	char *cmdname;
 
@@ -4139,6 +4139,7 @@ main(int argc, char **argv)
 			(void) fprintf(stderr, gettext("unrecognized "
 			    "command '%s'\n"), cmdname);
 			usage(B_FALSE);
+			ret = 1;
 		}
 		libzfs_mnttab_cache(g_zfs, B_FALSE);
 	}

cmd/zpool/zpool_main.c

@@ -3269,7 +3269,7 @@ print_scan_status(pool_scan_stat_t *ps)
 	 */
 	if (ps->pss_state == DSS_FINISHED) {
 		uint64_t minutes_taken = (end - start) / 60;
-		char *fmt;
+		char *fmt = NULL;
 
 		if (ps->pss_func == POOL_SCAN_SCRUB) {
 			fmt = gettext("scrub repaired %s in %lluh%um with "
@@ -4392,7 +4392,7 @@ int
 main(int argc, char **argv)
 {
 	int ret;
-	int i;
+	int i = 0;
 	char *cmdname;
 
 	(void) setlocale(LC_ALL, "");
@@ -4450,6 +4450,7 @@ main(int argc, char **argv)
 		(void) fprintf(stderr, gettext("unrecognized "
 		    "command '%s'\n"), cmdname);
 		usage(B_FALSE);
+		ret = 1;
 	}
 
 	libzfs_fini(g_zfs);

cmd/zpool/zpool_vdev.c

@@ -548,7 +548,7 @@ get_replication(nvlist_t *nvroot, boolean_t fatal)
 	uint_t c, children;
 	nvlist_t *nv;
 	char *type;
-	replication_level_t lastrep, rep, *ret;
+	replication_level_t lastrep = { 0 }, rep, *ret;
 	boolean_t dontreport;
 
 	ret = safe_malloc(sizeof (replication_level_t));